Entero-oxyntin, formerly called "intestinal gastrin" or the "intestinal phase hormone," originates in the small intestine and, when released, stimulates gastric acid secretion. This hormone is partially, or possibly entirely, responsible for the intestinal phase of gastric acid secretion. The objectives of the proposed project are to determine (1) the distribution of entero-oxyntin in the small intestine, (2) the role of intestinal distension alone and in combination with chemical stimulation on entero-oxyntin release, (3) the influence of vagal innervation on entero-oxyntin release from the intestine on its action on the stomach, (4) possible extragastric effects of the hormone, and (5) whether entero-oxyntin release and action is influenced by circulating amino acids. Recent studies have shown that entero-oxyntin can be distinguished from other acid-stimulating hormones which originate in the small intestine by its unique ability to potentiate the maximal Heidenhain pouch responses to pentagastrin and histamine in dogs. This assay of entero-oxyntin release will be used in dogs prepared with Heidenhain pouch, antrectomy, gastric fistula and an isolated pouch of the small intestine which we have developed and validated for its ability to release entero-oxyntin when perfused with liver extract.